3 All this may perhaps seem to you matter for jesting, seeing that you take so much pleasure in comedies and lyrics and mimes like those of Lentulus; although so blunted is your wit that I am not disposed to allow that you can understand even language so simple. You may treat the words of prophets with contempt, but Amos will still make answer to you: “Thus says the Lord, For three transgressions and for four shall I not turn away from him?” For inasmuch as Damascus, Gaza, Tyre, Edom, the Ammonites and the Moabites, the Jews also and the children of Israel, although God had often prophesied to them to turn and to repent, had refused to hear His voice, the Lord wishing to show that He had most just cause for the wrath that he was going to bring upon them used the words already quoted, “For three transgressions and for four shall I not turn away from them?”
It is wicked, God says, to harbour evil thoughts; yet I have allowed them to do so. It is still more wicked to carry them out; yet in My mercy and kindness I have permitted even this. But should the sinful thought have become the sinful deed? Should men in their pride have trampled thus on my tenderness? Nevertheless “I have no pleasure in the death of the wicked, but that the wicked turn from his way and live;” and as it is not they that are whole who need a physician but they that are sick, even after his sin I hold out a hand to the prostrate sinner and exhort him, polluted as he is in his own blood, to wash away his stains with tears of penitence.
But if even then he shows himself unwilling to repent, and if, after he has suffered shipwreck, he refuses to clutch the plank which alone can save him, I am compelled at last to say: “Thus says the Lord, For three transgressions and for four shall I not turn away from him?” For this “turning away” God accounts a punishment, inasmuch as the sinner is left to his own devices. It is thus that he visits the sins of the fathers upon the children unto the third and fourth generation; not punishing those who sin immediately but pardoning their first offenses and only passing sentence on them for their last.
For if it were otherwise and if God were to stand forth on the moment as the avenger of iniquity, the church would lose many of its saints; and certainly would be deprived of the apostle Paul. The prophet Ezekiel, from whom we have quoted above, repeating God's words spoken to himself speaks thus: “Open your mouth and eat what I shall give you. And behold,” he says, “an hand was sent unto me; and, lo, a roll of a book was therein; and he spread it before me; and it was written within and without: and there was written therein lamentations, and a song, and woe.” The first of these three belongs to you if you prove willing, as a sinner, to repent of your sins.
The second belongs to those who are holy, who are called upon to sing praises to God; for praise does not become a sinner's mouth. And the third belongs to persons like you who in despair have given themselves over to uncleanness, to fornication, to the belly, and to the lowest lusts; men who suppose that death ends all and that there is nothing beyond it; who say: “When the overflowing scourge shall pass through it shall not come unto us.” The book which the prophet eats is the whole series of the Scriptures, which in turn bewail the penitent, celebrate the righteous, and curse the desperate.
For nothing is so displeasing to God as an impenitent heart. Impenitence is the one sin for which there is no forgiveness. For if one who ceases to sin is pardoned even after he has sinned, and if prayer has power to bend the judge; it follows that every impenitent sinner must provoke his judge to wrath. Thus despair is the one sin for which there is no remedy. By obstinate rejection of God's grace men turn His mercy into sternness and severity. Yet, that you may know that God does every day call sinners to repentance, hear Isaiah's words: “In that day,” he says, “did the Lord God of Hosts call to weeping and to mourning and to baldness and to girding with sackcloth: and behold joy and gladness, slaying oxen, and killing sheep, eating flesh, and drinking wine; let us eat and drink, for tomorrow we shall die.”
After these words filled with the recklessness of despair the Scripture goes on to say: “And it was revealed in my ears by the Lord of Hosts, Surely this iniquity shall not be purged from you till you die.” Only when they become dead to sin, will their sin be forgiven them. For, so long as they live in sin, it cannot be put away.
Source: Letters (New Advent)